Arrangement for a steam-heated autoclave



Dec. 2, 1969 F. LINDER 3,481,592

ARRANGEMENT FUR A STEAM-HEATED AUTOCLAVE Filed DEC. 22, 1966 United States Patent 3,481,692 ARRANGEMENT FOR A STEAM-HEATED AUTOCLAVE Fritz Linder, Skarhamn, Sweden Filed Dec. 22, 1966, Ser. No. 603,811 Claims priority, application Sweden, Mar. 4, 1966,

,913/ 6 Int. Cl. A611 3/00, /00, 7/00 US. CI. 21-94 4 Claims ABSTRACT OF THE DISCLOSURE A steam operated autoclave having a circulating steam phase, a steam producing heat accumulator, a water container and valves in the conduits between the different parts of the autoclave and its accessories for controlling the flow of steam and water between the parts. Pressure and temperature sensing means are arranged to control the steam feed to the autoclave in such a way as to produce repeated pressure variations in the autoclave and thereby achieve an effective sterilization.

In conventional steam operated autoclave having a closed circuit for the purpose of supplying steam, the air in the autoclave is expelled together with condensed water formed in the autoclave through a common conduit connected to a water recipient. The water recipient is, by means of an evacuation conduit, connected to a valve which is adapted to be opened when air is present in the system and to be closed when passed through by steam. This known device is further provided with a feed conduit issuing from the recipient and being connected to the steam producer, said feed conduit provided with a valve by which the water quantity fed to the steam producer can be controlled so as to obtain the desired steam pressure in the autoclave. In this known device, a rather long sterilization time is required before all the air has been expelled and the desired sterilization temperature has been reached.

The purpose of the present invention is to produce automatically repeated, previously determined pressure variations during the operation of the autoclave where- 'by the air present in the autoclave is quickly and completely expelled and a very short sterilization time is achieved. By means of the very quick and repeated pressure variations thus obtained, the germs are effectively killed. The invention is thus based on the following knowledge. The core of the bacterium cell is protected by a membrane which is compressed at a pressure increase in the autoclave, causing the pressure in the bacterium to be raised.

Any succeeding quick pressure release then occurring in the autoclave will cause a very quick expansion of the membrane due to the high pressure in the bacterium. This causes a burst of the membrane, with the cell core of the' bacterium coagulating at the high temperature.

In accordance with the invention, the above require ments are fulfilled and a sterilization procedure with predetermined pressure variations is obtained, by pressure and/0r temperature sensing means arranged so as to "ice operate the valve in the feeding conduit to control the steam feeding. 'Also a three-way valve is arranged between the autoclave and the water container and is adapted to connect the water container alternatively with the autoclave and the atmosphere. The autoclave is hereby therefore connected to the water container on the one hand through a connection in which the three-way valve is included for removal of condensed water formed in the autoclave and on the other hand by means of a connection for the exhaust of air andv steam.

In order that the invention will be fully understood, reference will now be made to the accompanying drawing which forms part of this specification and shows diagrammatically a device according to the invention.

Reference numeral 1 denotes an autoclave which by means of a conduit 2 is connected to a heat accumulator 3 serving as a steam producer, and the temperature is kept at a constant value in the heat accumulator by means of a thermostat 4 in the same.

The heat accumulator 3 is fed with water, to be evaporated, from a water container 5 through a feeding conduit 7 provided with a two-way valve 6, said conduit 7 debouching in the heat accumulator 3 with a spray mouth piece 8. The two-way valve 6 is in this case assumed to be in the shape of an electromagnetic valve. Condensed water formed in the autoclave 1 is drained through a conduit 9 connected to the bottom of the autoclave, said draining conduit 9 being connected through a three-way valve 10 and a conduit 11 to the water container 5. The three-way valve 10, which is assumed to take the shape of an electromagnetic valve, also connects the conduit 1.1 from the water container 5 to a water storage tank 12 via conduits 13 and 14 for filling the water container 5 with water. The bottom of the autoclave is further provided with an evacuation conduit 15 having a thermometer 16, a thermostat 17 and a pressure switch 18. The evacuation conduit 15 is connected to the water storage tank 12 via a conduit 20 provided with a selector valve 19, the last mentioned conduit 20 debouching above the water level in the storage tank v12. The evacuation conduit 15 is further provided with a branch conduit 21 connected to the water container 5, and the conduit 14 extending from the three-way valve 10 is, by means of a conduit 22, connected to the conduit 20. In a way known per se, the evacuation conduit 15 also contains a safety valve 23. So as to prevent an entering of the steam into the storage tank 12 the conduit 14 is provided with an one-way valve 24. The pressure and temperature sensing means in the evacuation conduit 15 are preferably arranged in the close neighbodhood of the autoclave 1. t

The thermostat 17 and the pressure switch 18 are intended to control electrically the three-way valve 10 and the two-way valve 6. When the solenoid 10a of the threeway valve 10 conducts electric current, the valve opens the connection between the autoclave 1 and the water container 5 via the conduits 9 and 11 and closes simultaneously the connection between the water container 5 and the storage tank 12 via the conduits 11, 13 and 14. When the solenoid 10a of the three-way valve 10 does not conduct any electric current, the condition will be the reversed one, i.e. the connection between the autoclave .1 and the water container 5 is closed and instead the connection is opened between the water container 5 and the water storage tank 12.

The two-way valve 6 in the feeding conduit 7, this valve 6 controlling the water supply to the heat accumulator 3, is opened and closed when the electric current to the solenoid 6a of the two-Way valve 6 is connected and interrupted, respectively.

The pressure switch 18 and the thermostat 17 are preferably adjusted in a predetermined pressure and temperature range, respectively.

The arrangement just described operates as follows.

At first, when the air in the autoclave 1 is to be expelled and the pressure raised, the pressure switch 18 operates to feed electric current to the solenoid 6a of the two-way valve 6 and the solenoid 10a of the three-way valve 10, which causes the two-way valve 6 to open the connection between the water container 5 and the heat accumulator 3 and the three-way valve to open the connection between the autoclave 1 and the water container 5, simultaneously as the connection between the conduit 11 and the conduit 13, 14 connected to the storage tank 12 is closed. When the two-Way valve 6 is opened, water streams from the water container 5 through the feeding conduit 7 into the heat accumulator 3 via the spray mouth piece 8. The water is quickly evaporated in the heat accumulator 3 which preferably is held at a constant temperature of 250 C., and the steam thus produced streams through the conduit 2 to the autoclave 1. The water condensed during the heating of the autoclave is drained to the water container 5 through the drainage conduit 9 and the conduit 11 via the three-way valve 10.

The air present in the autocalve 1 is expelled by means of the steam entering the autoclave, and streams, together with the steam, out of the autoclave through the evacuation conduit 15, the selector valve 19 then being open and further through the conduit 20 to the storage tank 12 which is in direct connection with the atmosphere. As soon as the greater part of the air has been expelled from the autoclave 1 and has passed the selector valve 19, the succeeding steam stream will influence this valve in such a way that it automatically closes.

A temporarily closed circulation system is thereby obtained whereby the pressure in the autoclave 1 will quickly increase. For the reason that the autoclave 1 is in direct connection with the water container 5 through the evacuation conduit and the branch conduit 21 from the same, the pressure in the autoclave 1 will momentarily be transmitted to the water surface in the water container 5 to force the water to stream with increased speed to the heat accumulator 3 to be evaporated. From the accumulator it is sprayed, in the form of steam, into the autoclave causing a continuous pressure increase. The pressure in the autoclave is increased in this manner to the maximum value pre-set by means of the pressure switch 18 which then interrupts the electric current to the solenoid 6a of the two-way valve 6 and the solenoid 10a of the threeway valve 10 such that the two-way valve 6 is closed and the water supply to the heat accumulator 3 ceases. Simultaneously, the three-way valve 10 closes the connection between the autoclave 1 and the water container 5 and opens instead the connection between the conduit 11 and the conduit 13, 14 connected to the storage tank 12, whereupon the air residues present in the autoclave 1 and the conduits are brought along by the steam streaming with a high speed. In case the selector valve 19, which preferably is provided with cooling fins, is cooled during the sterilization proper, this valve is opened for removal of a part of the air but is closed thereupon by the succeeding steam stream. The pressure in the autoclave 1 then drops quickly via the evacuation conduit 15, the branch conduit 21, the water container 5, the conduit 11, the three-Way valve 10 and the conduits 13, 22 and 20. When the pressure in the autoclave has dropped to the minimum valve which has been pre-set by means of the pressure switch 18, the latter will be reactuated so that the solenoid 6a of the two-Way valve 6 and the solenoid 10a of the three-way valve 10 again will conduct electric current and the pressure will again rise and any formed condensed water will be drained to the water container 5 as already described.

This sterilization procedure with increasing and decreasing pressure is repeated automatically several times until all the air has been removed from the autoclave and the maximum temperature pre-set by means of the thermostat 17 is reached. This maximum temperature preferably corresponds to a pressure for dry saturated steam which is somewhat below the minimum pressure pre-set on the pressure switch 18. By means of this adjustment possibility, it is inter alia ensured that all the air is removed from the autoclave when the maximum temperature has been reached.

When the maximum temperature has been reached, the thermostat 17 controls the continued sterilization procedure. The thermostat then cuts oil the current to the two-way valve 6, which then closes and cuts off the water feeding to the heat accumulator 3, and feeds the threeway valve 10 with current whereas the connection of the autoclave 1 with the conduit 13 is interrupted and the system is closed. Because of a certain heat radiation from the autoclave the temperature drops in the same and when the temperature has dropped to the minimum temperature pre-set by means of the thermostat, the thermostat 17 connects the electric current to the two-way valve 6 which thereby is opened such that water again is passed to the heat accumulator 3 to be evaporated. The temperature and the pressure in the autoclave are increased in this manner until the reaching of the maximum temperature pre-set by means of the thermostat, whereupon the thermostat again interrupts the electric current feed to the two-way valve 6 which thereby is closed and thus the steam feeding ceases.

The sterilization continues until a timer, not shown in the drawing, interrupts the electric current to the thermostat 17 and the pressure switch 18, the desired sterilization time being adjusted on this timer. Thereupon the three-way valve 10 cuts off the connection between the conduit 9 and the conduit 11 and instead opens the connection between the conduit 11 and the conduit 13.

The pressure in the autoclave 1 will then quickly drop via the evacuation conduit 15, the branch conduit 21, the water container 5, the conduit 11, the three-way valve 10 and the conduits 13, 22 and 20. The one-way valve 24 prevents steam from entering the storage tank 12. When pressure equilibrium has been reached, the one-way valve 24 will automatically be opened by the pressure from the water column in the storage tank 12 such that water will stream from the storage tank 12 to the water container 5 via the conduit 14, the conduit 13, the three-way valve 10 and the conduit 11, whereby the air present in the water container 5 is pressed through the conduit branch 21, the selector valve 19 now open, and the conduit 20 out to the atmosphere. The water present in the conduit 11 and the conduit 13 after the filling of the container 5 will at the succeeding sterilization be pressed back to the storage tank 12 via the conduit 22 and the conduit 22 and the conduit 20. The sterilization procedure may also be controlled by one or several pressure switches and/or thermostats. By providing one thermostat and two pressure switches, an advantage is realized in that very small pressure variations are obtainable. In this case, one of the pressure switches is set on the desired maximum pressure and the other pressure switch is set on the desired minimum pressure.

As examples of pressure and temperature values used in the practice of the sterilization procedure, the following values may be mentioned. The pressure switch 18 can be adjusted to interrupt the current circuit at a maximum pressure in the interior of the autoclave of 2.5 atmospheres gauge and to close the current circuit again at a minimum pressure of 1.5 atmospheres gauge. The thermostat 17 can be :provided to operate at a maximum temperature of about 136 C. and a minimum temperature of about 132 C. in the interior of the autoclave 1. The temperature of 138 C. corresponds to a steam pressure in the autoclave of 2.5 atmospheres gauge and the temperature of 132 C. corresponds to a steam pressure of 2 atmospheres gauge in the interior of the autoclave when the latter does not contain any air. A condition of dry saturated steam is thus maintained in the autoclave.

When sterilizing textile products which contain air, the cycle described above is automatically prolonged by means of further pressure variations for the reason that the adjustment of the thermostate is retarded because of the small amount of air collected in the tube which contains the body sensing the temperature. Consequently, the thermostat 17 will switch over before the pressure switch 18 which causes a further pressure drop. This means that the timer (not shown) and the selector valve are spared. The sterilization time is automatically prolongedin rerelation to the quantity of air present and the number of pressure variations is increased which is to be considered as an advantage and which is desired.

The sterilization of instruments, which are inserted into the autoclave by being placed freely on a tray, can be carried out after only three pressure variations, but the sterilization of textile products requires, as has been proved by experiments, about six pressure variationsThe whole sterilization time requires not more than about 2-4 minutes with an autoclave according to the present invention.

The interconnection of the electric devices is not shown in detail in the drawing for the reason the circuit diagram surely is quite clear to anyone skilled in the art, and because the electric circuitry is not included within the scope of this invention.

The invention is not restricted to the embodiments shown and described and many modifications could be carried out within the scope of the appended claims. Thus the conduit 9 may be excluded and furthermore the pressure and/or temperature sensing means may be situated in other preferred positions in the system.

I claim:

.1. In a steam operated sterilization system having a circulating steam phase, the combination comprising:

an autoclave,

a heat accumulator for producing steam, the heat accumulator being operatively connected to communicate with the interior of the autoclave,

a water container located exteriorly of the autoclave and operatively connected to the heat accumulator, the water container further being operatively connected to communicate with the interior of the autoclave,

a two-way valve interposed between the water container and the heat accumulator for controlling the flow of water to the heat accumulator,

a three-way valve interposed between the autoclave and the water container for selectively connecting the water container to the autoclave and to the atmosphere,

a water storage means operatively connected to the water container for automatic compensation of water losses after each sterilization, and

pressure and temperature sensing means operatively connected to the interior of the autoclave and to the two-way and three-way valves for selectively opening and closing the two-way and three-way valves in response to pressure and temperature conditions within the autoclave to produce repeated, predetermined pressure variations within the autoclave.

2. A steam operated sterilization system according to claim 1, in which the connection between the water container and the autoclave including the three-way valve, is adapted to carry water condensed in the autoclave to the water container, and in which the water container is further operatively connected to the autoclave through a connection for expelling air and steam from the autoclave.

3. A steam operated sterilization system according to claim 2, in which the connection between the autoclave and the water container 'for expelling air and steam from the autoclave comprises an evacuation conduit operatively connected to communicate with the interior of the autoclave and a branch conduit extending from the evacuation conduit to the water container.

4. A steam operated sterilization system according to claim 2, in which the water storage means includes a water storage tank, and in which the connection between the autoclave and the water container for expelling air and steam from the autoclave comprises an evacuation conduit operatively connected to communicate with the interior of the autoclave and a branch conduit extending from the evacuation conduit to the water container, the evacuation conduit being in communication with the water storage tank through a conduit extending from the evacuation conduit and including a temperature-actuated selector valve; the evacuation conduit being further in communication with said water storage tank through a circuit including, in the sequence presented; the water container, the three-way valve and a conduit extending from the three-way valve to the water storage tank.

References Cited UNITED STATES PATENTS 1,728,333 9/1929 Crowther 2160 1,728,334 9/1929 Crowther 2160 XR 3,107,975 10/1963 Linder 21104 XR MORR'IS O. WOLK, Primary Examiner BARRY S. RICHMAN, Assistant Examiner US. Cl. X.R. 

